This invention relates generally to communication systems and more particularly to radio transceivers used within such communication systems.
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and share information over that channel. For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication session between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver receives RF signals, removes the RF carrier frequency from the RF signals directly or via one or more intermediate frequency stages, and demodulates the signals in accordance with a particular wireless communication standard to recapture the transmitted data. The transmitter converts data into RF signals by modulating the data in accordance with the particular wireless communication standard and adds an RF carrier to the modulated data in one or more intermediate frequency stages to produce the RF signals.
As the demand for enhanced performance (e.g., reduced interference and/or noise, image rejection, improved quality of service, compliance with multiple standards, increased broadband applications, et cetera), smaller sizes, lower power consumption, and reduced costs increases, wireless communication device engineers are faced with a very difficult design challenge to develop such a wireless communication device. Typically, an engineer is forced to compromise one or more of these demands to adequately meet the others. For instance, an engineer may choose a direct conversion topology (i.e., convert directly from an RF signal to a base-band signal or directly from a base-band signal to an RF signal) to meet size requirements and/or broadband application requirements. However, for direct conversion transceivers, noise and/or interference increases due to local oscillation leakage, imaging problems, non-linearities due to component mismatches and/or process variations are more detrimental to overall performance are more pronounced.
As is known, local oscillation leakage results from I-Q DC offset and imperfections of the mixers within a transmitter that allow the local oscillation, which equals the RF, to be present in the resultant RF signal. The local oscillation leakage can be minimized by using multiple IF stages within the transmitter. In such an implementation, each IF stage uses a local oscillation that has a significantly different frequency than the RF, with the sum of the multiple local oscillations equals the RF. Since each local oscillation has a significantly different frequency than the RF, each local oscillation is outside the RF band of interest (i.e., the frequency spectrum of the resulting RF signal). But this requires an abandoning of the direct conversion topology and its benefits with respect to size reduction, power consumption reduction, reduced costs, and reduced complexity for broadband applications.
Therefore, a need exists for a low power, reduced size, reduced cost, and robust performance direct conversion topology radio, radio transmitter, radio receiver, and/or components thereof.
These needs and others are substantially met by the radio having a self-calibrating transmitter. The radio includes a transmitter section, mixer, analog receiver section, calibration switch module, digital receiver section, calibration determination module, and calibration execution module. The transmitter section produces a modulated radio frequency (RF) signal based on an I-component and Q-component of a base-band signal and an I-component and Q-component of a transmitter local oscillation.
The mixer is operably coupled to mix the modulated RF signal with an I or Q component of the transmitter local oscillation to produce a base-band representation of the modulated RF signal.
The calibration switch module is operably coupled to the analog receiver section and the digital receiver section. When the radio is in normal mode, the calibration switch module outputs analog low IF signals, which are produced by the analog receiver section, to the digital receiver section for recapturing the embedded data. During calibration mode, the calibration switch module provides the base-band representation of the modulated RF signal to the digital receiver section.
In calibration mode, the digital receiver section produces a 2nd base-band digital signal from the base-band representation of the modulated RF signal. The calibration determination module interprets the 2nd base-band digital signal to produce a calibration signal. Such a determination is based on analyzing the frequency spectrum of the 2nd base-band digital signal to determine local oscillation leakage and imbalances within the transmitter. Accordingly, the calibration signal is generated to minimize local oscillation leakage and/or imbalances within the transmitter.
The calibration execution module is operably coupled to calibrate the DC level of the I and/or Q component of the base-band signal and/or the gain of the I and Q component of the base-band signal in accordance with the calibration signal to reduce imbalances within the transmitter section.